The present invention relates to wheel alignment machines for motor vehicles and more specifically to such a machine having the ability to more accurately measure the dynamic forces acting between a vehicle wheel assembly and the surface engaged thereby thus enabling alignment adjustments to more completely compensate for these forces.
In manufacturing and assembly of motor vehicles, wheel alignment quality improvement demands by customers has steadily increased in recent years. Wheel alignment problems may exhibit themselves in various ways such as by the need for the driver to maintain a force on the vehicle steering wheel to maintain straight line tracking of the vehicle, excessive or rapid tire wear or even reduced fuel economy resulting from increased rolling resistance of the tire. Vehicle manufacturers typically have wheel alignment complaints in the top ten of their repetitive warranty problems.
Unfortunately, achieving correct wheel alignment is a very complex problem to resolve due to the wide variety of factors affecting wheel alignment in a given vehicle with a given set of wheel/tire assemblies. These factors include the specific wheel assembly geometry that affect caster, camber, and toe in/toe out of the vehicle. Generally, these are the factors which are and have been measured by current wheel alignment apparatus. However, there are also a number of other factors that contribute significantly to vehicle performance and may vary from one vehicle to the next of identical design. Among these additional factors are the dynamic tire forces such as conicity, and ply-steer which may dramatically influence the handling of a given vehicle. These factors will vary from one tire to the next even when the tires selected for a vehicle may have been manufactured at the same location and time and even using the same tire mold.
Conventional geometrical alignment apparatus utilized by the motor vehicle manufacturers is not able to measure these dynamic tire forces and hence alignment adjustments are not able to be made to compensate for these forces.
Further complicating the problems in achieving proper and accurate wheel/tire alignment on a motor vehicle is the need for any such force measuring apparatus to determine the dynamic forces rapidly so as to accommodate the needs of motor vehicle manufacturers"" high speed assembly lines.
The present invention, however, provides apparatus which is well suited for detecting and accurately measuring these dynamic tire forces and, when used in an alignment application, is able to facilitate alignment adjustments to minimize these forces by netting the resultant forces on a given axle to or closely approximating zero.
The present invention comprises an arrangement for supporting a vehicle wheel/tire assembly by means of a pair of rollers, each of which is independently movable laterally with respect to the wheel/tire assembly. Further, the roller assembly is supported on support frame which in turn is movably supported on a base structure to allow relatively free movement of the frame along both an X axis and Y axis so as to thereby enable rotational movement of the support frame about the Z axis. In this regard, it should be noted that throughout this specification, the X axis is considered to correspond to a horizontal axis extending parallel to the motor vehicle longitudinal axis, the Y axis is considered to correspond to a horizontal axis but extending perpendicular to the X axis and the Z axis is a vertical axis extending perpendicular to the plane defined by the Xxe2x88x92Y axis.
By supporting the rollers in such a manner so as to allow relatively free independent movement thereof, the dynamic tire forces exerted thereon during rotational movement of the wheel/tire assembly will effect relative movement between the respective rollers as well as between each roller and the wheel/tire assembly. The extent of this movement will provide a measurement of the dynamic tire forces which measurements may then be utilized for tire sorting/matching or when the apparatus is used in an alignment operation, to enable adjustment of the vehicle wheel alignment to achieve a substantially zero net force or some predetermined net force as desired.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.